In current practice, there exist numerous situations in which it is desirable to efficiently separate fluids such as whole blood into two or more specific components (e.g. plasma, red blood cells, leukocytes, platelets, etc.). In commercial applications, it is often necessary to separate whole blood into two or more constituents in order that a specific blood constituent may be harvested and utilized for the preparation of medically useful blood derivatives or preparations (e.g. packed red blood cells, fresh frozen plasma, specific blood factors, etc.). Also, in therapeutic settings it is often desirable to separate whole blood into two or more constituents for purposes of treating or removing a specific constituent(s) of the blood in accordance with certain therapeutic protocols.
In almost all blood constituent separation procedures, whether commercial or therapeutic, quantities of whole blood are withdrawn from a human subject, the whole blood is then separated into two or more constituent fractions and at least one of the constituent fractions is subsequently transfused back into the human subject. The nonreinfused constituent fraction(s) may be retained for use in the preparation of various blood plasma products (e.g. fresh frozen plasma, albumin, or Factor VIII) or, in the therapeutic applications, may be discarded and replaced by plasma from a healthy donor or may be subjected to physical pharmacologic or radiologic treatment and subsequently returned to the human subject.
The general term "apheresis" used to describe three-step procedures wherein whole blood is a) withdrawn, b) separated into fractions and c) at least one of the fractions is retransfused into the human subject. Specific types of apheresis procedures include: "plasmapheresis" (for the collection of blood plasma), "leukapheresis" (for the collection of leukocytes), "thrombocytapheresis" (for the collection of platelets), therapeutic plasma exchange (wherein a portion of the subject's blood plasma is replaced with other fluids, such as plasma obtained from another human), and therapeutic plasma processing wherein a portion of the subject's plasma is separated, treated or processed and then returned to the subject.
Prior to the 1970's, when it was desired to separate whole blood into specific blood constituent(s), it was generally necessary to draw, on a unit by unit basis, quantities of whole blood from a human donor. Each unit of whole blood withdrawn was manually centrifuged to effect separation of the desired blood constituent or component and, thereafter, the remaining portions of the blood were manually reinfused into the donor. It was typically necessary to repeat such a procedure, on the same donor, several times (i.e. unit after unit) until the maximum allowable volume of plasma or other blood constituent had been collected.
More recently, automated apheresis machines been developed to minimize the degree of manual endeavor required when separating and collecting specific blood constituents. These automated apheresis machines typically comprise a central computer electrically connected to, and programmed to control, a system of tubes, vessels, filters and at least one blood separation device. The blood separation device is typically a rotating centrifugal filter or membrane which operates to separate the desired specific blood constituent(s) (e.g. plasma, cells, platelets, etc.). The typical automated apheresis machines of the prior art incorporate one or more "peristaltic pumps" or "tubing pumps" for moving blood, blood constituents and/or reagent solutions through the machine. Such "peristaltic pumps" or "tubing pumps" generally consist of a series of rotating rollers or cams over which a length of plastic tubing is stretched. Rotation of the cams or rollers then serves to dynamically compress regions of the tubing so as to move the desired fluids through the tubing at a desired rate. The use of such peristaltic pumps is particularly suitable in automated apheresis equipment because the mechanical working components of such pumps do not come in contact with the blood or other fluids being pumped, thereby preventing contamination of such fluids. Moreover, the use of peristaltic pumps permits intermittent disposal and replacement of the attendant tubing, as is commonly done to maintain sterile and hygienic conditions during each blood donation procedure. These peristaltic pumps are, however., given to a great deal of uncertainty or "drift" in calibration. Such uncertainty or "drift" in the pump calibration occurs because of variations in the size and material consistency of the pump tubing, variations in the rotational speed of the pump cam or rollers, stretching and/or wear of the pump tubing, etc. The resultant variations in the throughput of the peristaltic pumps complicates the operation of automated apheresis machines because such variations in pump throughout render it difficult to accurately control volume of blood or blood constituents collected in a particular procedure. Strict control of the volumes of blood or blood constituents withdrawn is required by governmental regulation intended to prevent inadvertent or purposeful over-withdrawal of blood or specific blood constituents from the human subject, as may result in injury to the human subject. Furthermore, variations in throughput of the pumps is problematic because many steps in automated apheresis procedures require precise knowledge of actual fluid flow rates. Also, certain system components, such as the separator device 20 require pressure and flow control in order to operate safely and efficiently.
In view of the above-stated shortcomings of the prior art automated apheresis machines, there exists a need for new apheresis machines and/or methods which minimize the expense and/or complexity of apheresis procedures, without any prohibitive diminution in the ability to monitor and maintain accurate control of the calibration and throughput of the blood and other fluids being extracted from the human subject and processed by the apheresis machine.